1. Field of the Invention
The present invention relates to a film cartridge holding device in the film cartridge chamber of a camera.
2. Description of Related Art
A common type of film cartridge used to protect camera film from light and other foreign material has a roughly cylindrical outer shell and a spool shaft extending through the center of the outer shell. The film is wound around the spool shaft and extends out of the film cartridge through a slot in the outer shell. When the film is to be exposed in a camera, the film cartridge is loaded into the camera. To help control the movement of film into and out of the film cartridge, cameras generally have a device for holding the film cartridge within the camera.
One type of mechanism for holding a film cartridge in a fixed position in a camera engages with the outer shell of the film cartridge. This mechanism prevents the outer shell from moving within the camera, but the position of the spool shaft is not controlled.
Another type of device supports the two ends of the spool shaft of the film cartridge by a pair of holding shafts, as shown in Japanese Unexamined Patent Publication Hei 4-234744. Because this mechanism directly holds the ends of the spool shaft, the spool shaft is precisely positioned. Consequently, when the spool shaft rotates to scroll the film out of the cartridge, smooth film supply results since vibration of the spool shaft and the film is suppressed. Please refer to U.S. Pat. No. 5,296,887, herein incorporated by reference.
When a pair of holding shafts are utilized to position the ends of the spool shaft, one of the holding shafts acts as the spool driving shaft. The spool driving shaft rotates the spool shaft to forward and rewind the film in the camera. The spool driving shaft has an engagement part (e.g., a key) which engages a groove formed on the spool shaft end.
However, when the film cartridge is loaded into a cartridge chamber in a camera, the engagement part on the spool driving shaft must align with the groove in the spool shaft end to allow the film cartridge to be fully inserted into the camera. Typically, the spool driving shaft is withdrawn from the cartridge chamber by a camera user when a film cartridge is inserted into the cartridge chamber. Once the film cartridge is fully inserted into the cartridge chamber, the user rotates the spool driving shaft while forcing the spool driving shaft into the cartridge chamber. Rotating the spool driving shaft aligns the key on the spool driving shaft with the groove in the spool shaft end. When the key and groove are aligned, the spool driving shaft can be fully inserted into the cartridge chamber.
However, because the position of the spool shaft is not precisely controlled when the spool driving shaft is inserted into the cartridge chamber, the spool driving shaft and the other holding shaft do not always smoothly socket-connect with the ends of the spool shaft. In addition, play in the spool driving shaft increases the amount of backlash in the spool drive mechanism, which prevents precise positioning of the spool shaft.